Drawn yarns made of polyglycolic acid-based resins are excellent in mechanical strength and have biodegradability and bioabsorbability. Hence, the drawn yarns have conventionally been used as surgical sutures in the medical field and the like. In addition, since polyglycolic acid-based resins exhibit fast hydrolyzability under high temperature environments, applications of fibers made of polyglycolic acid-based resins to a drilling or completion field of oil recovery and the like have also been studied.
Conventional drawn yarns made of a polyglycolic acid-based resin are produced by the spinning drawn yarn method (SDY method) or by a two-step production method in which an undrawn yarn is fabricated by discharging a molten polyglycolic acid-based resin through a spinneret followed by rapid cooling, and subsequently the undrawn yarn is drawn. The latter method is efficient in mass production, but has the problems that the undrawn polyglycolic acid-based yarns agglutinate, so that the undrawn polyglycolic acid-based yarns cannot be drawn due to deterioration in the releasing properties at drawing, and that the obtained drawn yarns have a large single yarn fineness, and do not have a sufficiently high strength and a sufficiently high elongation, when the operational environment temperature or the temperature and humidity during storage are high.
In addition, Japanese Unexamined Patent Application Publication No. 2004-250853 (PTL 1) discloses a suture fiber made of a copolymer of glycolide and lactide, and a method for producing the suture fiber. In the production method, filaments discharged through a spinneret maintained at a temperature which is higher than the melting point of the copolymer by 40 to 60° C. are in an atmosphere having a temperature of higher than the melting point of the copolymer by 60° C. or more for a distance of 15 to 50 cm from the spinneret. In such a case, a fiber having a high tensile strength and a high tensile elongation is obtained. However, the fibers obtained in examples of PTL 1 had single yarn finenesses of 2 denier or more, and no fiber was obtained which had a smaller single yarn fineness and had a high strength and a high elongation.
On the other hand, in examples of U.S. Pat. No. 6,005,019 (PTL 2), yarns made of a poly(glycolide-lactide) copolymer were produced by keeping filaments in an atmosphere having a temperature of 110° C. with heating to 100° C. near an outlet of a spinneret. However, the drawn yarn produced by keeping the filaments in an atmosphere having a temperature of 110° C. with the heating to 100° C. near the outlet of the spinneret is still insufficient in single yarn fineness and in tensile elongation.